Learn more

What causes breast cancer?

No one knows exactly what causes breast cancer, but we do know that certain risk factors – the things that increase a person's chance of getting a disease – are linked to breast cancer. Risk factors change depending on the type of cancer.

There are a number of risk factors, both controllable and uncontrollable, which may increase the chances of developing breast cancer. For instance, the risk factors associated with diet can be controlled, but risk factors such as a person's age or family history can't be changed.

While all women are at risk for breast cancer, the factors listed below are associated with an increased chance of developing the disease.

Major Risk Factors

GeneticsStudies show that between five percent and 10 percent of breast cancers appear to be linked to mutations in certain genes (specifically the BRCA1 and BRCA2 genes). If a woman has inherited a mutated gene from either parent, she is more likely to develop breast cancer. More than half of women with inherited mutations will develop breast cancer by the age of 70.

Strong family historyThe risk is higher among women whose close blood relatives have the disease. Having a mother, sister or daughter with breast cancer almost doubles a woman's risk, particularly if the relative was diagnosed before age 50. A family history of ovarian cancer also increases your risk of developing breast cancer.

Previous breast cancerHaving had cancer in one breast increases the risk of having it in the other.

Earlier radiation treatmentWomen who have had chest area radiation treatment have a significantly increased risk of breast cancer (e.g. mantle radiation for Hodgkin's lymphoma).